1. Field of the Invention
This invention relates to a coolant reservoir tank for use in a liquid cooling system.
2. Description of the Related Art
Recently, a cooling system in which cooling is carried out by circulation of coolant, such as cooled water, has been used for absorbing the heat generated in an electronic apparatus formed with electronic components such as semiconductor devices. Such a cooling system has been structured, for example, as shown in FIG. 1. In order to cool a plurality of electronic devices 15-1.about.15-4, a cooling system 17 comprising a plurality of cooling units 16, each of which is composed of pumps 13 for feeding coolant 3 and heat exchangers 14 for cooling the coolant 3 to the predetermined temperature, is provided. The coolant 3 reserved in a reservoir tank 10 is fed to the respective cooling units 16 through a plurality of feed pipes 11A; the coolant 3 cooled to a predetermined temperature by the heat exchangers 14 is supplied to the electronic devices such as LSI (Large Scale Integrated Circuit) from the cooling unit 16; and the coolant 3 which has cooled the electronic devices 15-1.about.15-4 is returned to the reservoir tank 10 through a plurality of return pipes 11B. Such a cooling unit 16 can be expanded depending on the installed number of the electronic devices 15-1.about.15-4 on requirement. Therefore, the reservoir tank 10 is commonly provided with a plurality of feed pipes 11A and return pipes 11B for the coolant. In such a structure where the cooling is carried out by feeding the coolant 3 cooled down to the predetermined temperature to the electronic devices 15-1.about.15-4, it is essential to keep the temperature of the coolant 3 to be fed from each cooling unit 15 at a temperature lower than the specified temperature in order to always cool sufficiently the electronic devices 15-1.about.15-4. However, since heat exchanging capacity of such cooling unit 15 is limited, if temperatures of coolant 3 supplied from the reservoir tank 10 to the respective cooling units 16 are not equal, temperatures of coolant 3 fed from the respective cooling units 16 are inevitably not equal. Accordingly, the coolant 3 fed to each of the electronic devices 15-1.about.15-4 may no longer be cooled below the predetermined temperature, thus some electronic devices cannot be sufficiently cooled.
Therefore, it is necessary to provide a cooling unit in which the temperatures of the coolant 3 supplied via the plural feed pipes 11A from the reservoir tank 10 are equal so that the coolant 3 to be supplied from the cooling unit 16 is always kept at the predetermined temperature or lower. However, the conventional reservoir tank 10 has a following problem.
A typical example of the conventional reservoir tank is shown in the sectional view of side elevation of FIG. 2. A bottom 20A of a cylindrical vessel 20 is provided with a plurality of outlets 22 and inlets 23. The outlets 22 are connected with feed pipes 11A-1.about.11A-N, respectively, while the inlets 23 with return pipes 11B-1.about.11B-N. At the center of the vessel 20, a strainer 21 is provided for removing undesirable particles in the coolant. The coolant 3 returned as indicated by arrow marks C via the inlets 23 and the return pipes 11B-1.about.11B-N is reserved in the reservoir tank 20 and the coolant 3 filtered by the strainer 21 is output as indicated by arrow marks B via the outlets 22 and the feed pipes 11A-1.about.11A-N. Therefore, in such a structure, a distance between the inlet 23-1 and the outlet 22-1, both provided in the vicinity of the center of vessel 20 is extremely short and distance between the inlet 23-2 and the outlet 22-2, both provided in the vicinity of the wall of vessel 20 is very long. Meanwhile, since the heat loads of the electronic devices 15-1.about.15-4 are not always equal, temperature difference is generated in the coolant returned via each inlet 23. In this case, temperature of coolant output from the outlet 22-1 is influenced very much by the temperature of the coolant returned to the inlet 23-1. On the other hand, temperature of coolant output from the outlet 22-2 separated far from the inlet 23-2 is not influenced so much by the temperature of the coolant returned to inlet 23-2. Accordingly, non-equal temperatures of the coolant returned from the plural inlets cause a temperature difference in the coolant output from each of the plural outlets. Therefore, there lies a problem in that some coolant temperatures of the coolant output from the cooling units 16 do not become lower than the predetermined value. Consequently, uniform cooling cannot be achieved.